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    A child receives a vaccination from a smiling healthcare worker.

    Is this child more fortunate than many children?
    ::这个孩子比很多孩子更幸运吗?

    You may not feel lucky to get a shot. But you are very lucky to be able to get vaccinations. In many parts of the world, children do not get routine vaccinations. In 2008, the World Health Organization (WHO) estimated that 1.5 million children under the age of 5 died from diseases that are preventable with vaccinations.
    ::获得疫苗也许你并不感到幸运。但是,你非常幸运能够获得疫苗。 在世界许多地区,儿童得不到常规疫苗。 2008年,世界卫生组织(世卫组织)估计有150万5岁以下儿童死于通过接种可以预防的疾病。

    Immunity and Vaccination
    ::豁免和疫苗接种

    In previous concepts, you learned about B and T cells , special types of white blood cells that help your body to fight off a specific . They are necessary when the body is fighting off an infection. But what happens to them after the pathogen has been destroyed?
    ::在先前的概念中,你学到了B和T细胞, 特殊类型的白细胞, 帮助你的身体对抗特定的血细胞。 当身体在抗感染时,它们是必要的。但是病原体被摧毁后它们会怎样呢?

    Most B and T cells die after an infection has been brought under control. But some of them survive for many years. They may even survive for a person’s lifetime. These long-lasting B and T cells are called memory cells . They allow the immune system to “remember” the pathogen after the infection is over. If the pathogen invades the body again, the memory cells will start dividing in order to fight the pathogen or disease.
    ::大部分B型和T型细胞在感染得到控制后死亡。 但其中一些细胞存活了多年。 它们甚至可以活到一个人的一生中。 这些长期的B型和T型细胞被称为记忆细胞。 它们允许免疫系统在感染结束后“记住”病原体。 如果病原体再次侵入身体,记忆细胞将开始分裂,以对抗病原体或疾病。

    These dividing cells will quickly produce a new army of B or T cells to fight the pathogen. They will begin a faster, stronger attack than the first time the pathogen invaded the body. As a result, the immune system will be able to destroy the pathogen before it can cause an infection. Being able to attack the pathogen in this way is called immunity .
    ::这些分解细胞将很快产生一支新的B或T细胞的军队来对抗病原体。 它们将开始比病原体第一次侵入身体时更快、更猛烈的攻击。 因此,免疫系统将能够摧毁病原体,然后才能造成感染。 能够以这种方式攻击病原体就被称为免疫。

    Immunity can also be caused by vaccination . Vaccination is the process of exposing a person to a pathogen on purpose in order to develop immunity. In vaccination, a modified pathogen is usually injected under the skin by a shot. Only part of the pathogen is injected, or a weak or dead pathogen is used. It sounds dangerous, but the shot prepares your body for fighting the pathogen without causing the actual illness. Vaccination triggers an immune response against the injected antigen . The body prepares "memory" cells for use at a later time, in case the antigen is ever encountered again. Essentially, a vaccine imitates an infection, triggering an immune response, without making a person sick.
    ::免疫是故意将一个人暴露于病原体以发展免疫的过程。在疫苗接种中,经改良的病原体通常通过射杀注射在皮肤下。只有部分病原体注射,或使用弱或死病原体。听起来很危险,但射杀可以使身体在不造成实际疾病的情况下与病原体抗争。接种会触发对注射抗原的免疫反应。身体准备“模拟”细胞,供日后使用,以防再次遇到抗原。基本上,疫苗模仿感染,触发免疫反应,不使人生病。

    In many countries, children receive their first vaccination at birth with the Hepatitis B shot, which protects infants from Hepatitis B, a serious liver disease. Before vaccines, many children died from diseases that vaccines now prevent, such as whooping cough, measles, and polio. Those same germs exist today, but because babies are now protected by vaccines, we do not see these diseases nearly as often. Diseases you have probably been vaccinated against include measles, mumps, and chicken pox.
    ::在许多国家,儿童出生时第一次接种乙型肝炎疫苗,该疫苗可以保护婴儿免受乙型肝炎这一严重的肝病的侵袭。 在接种疫苗之前,许多儿童死于疫苗现在预防的疾病,如百日咳、麻疹和脊髓灰质炎。 同样的细菌今天也存在,但是由于婴儿现在受到疫苗的保护,我们并不经常看到这些疾病。 你可能接种了麻疹、流行性腮腺炎和天花等疾病疫苗。

    How does a vaccine work? See How a Vaccine Works at and The History of Vaccines at .
    ::疫苗如何运作?

    Summary
    ::摘要

    • Immunity is the ability to resist a particular pathogen.
      ::豁免是指抵抗某一特定病原体的能力。
    • Vaccination is deliberate exposure to a pathogen in order to bring about immunity.
      ::接种疫苗是故意接触病原体,以获得豁免。

    Explore More
    ::探索更多

    Use the resource below to answer the questions that follow.
    ::利用以下资源回答以下问题。

    • What Is Immunity? at (1:23)
      ::什么是豁免?在(1:23)处。
    1. How do vaccines provide immunity? How is the immune response initiated by vaccines similar to the body's natural immune response?
      ::疫苗如何提供豁免?疫苗引起的免疫反应如何与人体的自然免疫反应相似?
    2. Why do some people decide to take vaccines rather than letting the body develop natural immunity?
      ::为什么有些人决定使用疫苗,而不是让机构发展自然豁免?

    Review
    ::回顾

    1. Define immunity.
      ::界定豁免。
    2. Define vaccination.
      ::界定疫苗接种。
    3. If you have been vaccinated against measles, you are unlikely to ever have the disease, even if you are exposed to the measles virus. How does this work?
      ::如果你接种了麻疹疫苗,即使你感染了麻疹病毒,也不太可能患上麻疹。这如何运作?